Device for eliminating rotating stall in axial-flow compressors



DEVICE FOR ELIIMINATING ROTATING STALL IN AXIAL-FLOW COMPRESSORS Filed April 15, 1955 NOV. 4, 1958 R Q BULLOCK ETAL 2,858,974

INVENTORS ROBERT Q BULLOCK MERLE 6. HUPPERT BY x 1 ATTORNEYS United States Patent DEVICE FOR ELIMINATIN G ROTATING STALL IN AXIAL-FLOW COMPRESSORS Robert 0. Bullock, Fairview Park, and Merle C. Huppert, Elyria, Ohio, assignors to the United States of America as represented by the Secretary of the Navy Application April 13, 1955, Serial No. 501,214

1 Claim. (Cl. 230-115) (Granted under Title 35, U. S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to a device for eliminating rotating stall in axial-flow compressors by blocking a portion of the inlet area.

It has been found that the inlet stages of an axial flow compressor are likely to be operating in a stalled condition at rotational speeds less than approximately seventy percent of design speed. Stall in the inlet stages generally results in rotating stall patterns which may excite resonant vibrations in the blades due to the periodic flow variations caused by the rotating stall.

The present invention, in its broadest aspect, increases the air velocity in the tip region of the rotor blades in the first few stages of the compressor. An important result of this increased velocity is the prevention of the noted stall condition. The increased velocity is obtained by blockage of the inlet annulus of the compressor in the hub region.

An object of the present invention is the provision of a means to eliminate rotating stall in an axial flow compressor.

Another object is to provide means to eliminate the blade vibration and poor off-design performance associated with compressor rotating stall, particularly at low and intermediate engine speeds.

A further object of the invention is the provision of means to increase the air velocity in the tip region of the rotor blades.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

Fig. l is an axial sectional View of an air compressor comprising a preferred embodiment of the invention and Fig. 2 is a sectional view of the compressor shown in Fig. 1 and looking in the direction of the arrows 22.

Referring now to the drawings, wherein like reference characters designate like or corresponding parts throughout the several views, there is shown in Fig. 1 an axial compressor having a rotor 12 mounted on a rotor shaft 14. Rotor blades 16 are carried by rotor 12, and pass between stator blades 18 carried by casing 20. Upstream of the rotor blades 16 and stator blades 18 are inlet guide vanes 22.

Upstream of the guide vanes 22 there is provided a baffle 24 mounted on the hub 26 by meansof hinges 28. Battle 24 comprises a plurality of individual plates, as may be seen from Fig. 2, and each of these plates is conveniently pivoted about its hinge 28 by means of a tie rod 30 passing through a slot 32 in the hub 26. The tie rods 30 may conveniently be adjusted by means of a nut 34 in a central recess 36, the nut 34 having a bolt 38 ICC threaded through it. Upon rotation of bolt 38, nut 34 will be moved axially, and will thus serve to adjust the angle of the plates of baflle 24, and consequently the area blocked by the bafile.

By causing the plates of bafile 24 to extend into the air stream, the velocity of the air in the tip region of the rotor blades 16 is increased when the compressor is operating at speeds below its design speed. The increased velocity prevents stall in the tip region of the rotor blades. The flow disrupted by the baffle near the hub is free of periodicity. The entire flow has no periodic variations; thus, the problem of blade vibration is overcome. Additionally, this invention may also be used as a thrust controller when the compressor is part of an engine,

since by extending the baffle 24 into the airstream at de sign engine speed the air flow through the engine and the compressor pressure ratio are reduced. Hence, engine thrust is reduced without reducing engine speed.

It will be understood that the amount of blockage caused by the extension of bafile 24 may extend over a wide range, the adjustment of the blocking in the attached drawing being preferably approximately 20 percent of the total annular inlet area at the station. Adjustment of the baflie 24 is preferably made in accordance with compressor speed, and may be effected automatically by a servo-system.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claim the invention may be practiced otherwise than as specifically described.

What is claimed is:

In an axial flow compressor having rotor blades, and stator blades and subject to rotating stall, means to avoid and eliminate rotating stall in the compressor blading comprising a bafile upstream of the first row of blades, said baflle comprising a plurality of plates lying concentrically about the periphery of a hub, each plate being pivotally attached to said hub by hinge means connected to the upstream edge of each plate and to said hub, cylindrical threaded means rotatably mounted in a centrally located recess in said hub and located concentrically with the longitudinal axis of said hub, positioning means having a threaded opening therethrough being engaged with said threaded means for relative rotation therewith and being movable transversely of said threaded means upon rotation of said threaded means and strut means extending between each of said plates and said positioning means through radially directed openings in said hub extending from said recess through the surface of said hub and being pivotally connected to said plates and said positioning means whereby upon rotation of said threaded means in one direction said positioning means will be moved along said threaded means to adjust the angle of said plates through said strut means to move each of said plates about its hinge to cause said plates to move outwardly into the compressor inlet annulus whereby said plates partially block the inlet annulus ad jacent said hub and upon rotation of said threaded means in the reverse direction said plates will be caused to move inwardly against said hub.

References Cited in the file of this patent FOREIGN PATENTS 1,496 Great Britain Nov. 14, 1912 260,995 Italy, Oct. 25, 1928 463,657 Italy May 21, 1951 694,127 Great Britain July 15, 1953 702,266 Great Britain Jan. 13, 1954 1,010,604 France Mar. 26, 1952 

